Method for producing a single crystal

ABSTRACT

A method for producing a single crystal by Czochralski method with pulling a seed crystal from a raw material melt, wherein in which a range of a pulling rate of pulling a single crystal, a temperature gradient at a solid-liquid interface and a highest temperature at an interface between a crucible and a raw material melt are defined. The single crystal is pulled with controlling the pulling rate and/or the temperature gradient at a solid-liquid interface within the determined range. The method produces a single crystal in which a desired defect region and/or a desired defect-free region can be determined more precisely and a single crystal with desired quality can be more surely pulled.

TECHNICAL FIELD

The present invention relates to a method for producing a single crystalby Czochralski Method, more particularly, to a method for producing asingle crystal occupied by a desired defect region and/or a desireddefect-free region.

BACKGROUND TECHNOLOGY

A single crystal used as a substrate of semiconductor devices is, forexample, a silicon single crystal. It is mainly produced by CzochralskiMethod (referred to as CZ method for short hereafter).

When producing a single crystal by CZ method, for example, an apparatus1 for producing a single crystal as shown in FIG. 2 is used to producethe single crystal. This apparatus 1 for producing a single crystal hasa member for containing and melting a polycrystalline material such assilicon, heat insulating members to insulate heat, and etc. They areinstalled in a main chamber 2. A pulling chamber 3 extending upwardly iscontinuously provided from a ceiling portion of the main chamber 2, anda mechanism (not shown) for pulling a single crystal 4 by a wire 5 isprovided above it.

In the main chamber 2, a quartz crucible 7 for containing a melted rawmaterial melt 6 and a graphite crucible 8 supporting the quartz crucible7 are provided, and these crucibles 7 and 8 are supported by a shaft 9so that they can be rotated and moved upwardly or downwardly by adriving mechanism (not shown). To compensate for decline of the meltlevel of the raw material melt 6 caused by pulling of the single crystal4, the driving mechanism for the crucibles 7 and 8 is designed to risethe crucibles 7 and 8 as much as the melt level declines.

And, a graphite heater 10 for melting the raw material is provided so asto surround the crucibles 7 and 8. A heat insulating member 11 isprovided outside the graphite heater 10 so as to surround it in order toprevent that the heat from the graphite heater 10 is directly radiatedon the main chamber 2.

Moreover, a cooling cylinder 12 to cool a pulled single crystal isprovided and at the bottom of it a graphite cylinder 13 is provided. Acooling gas is flowed downward from top through these cylinders so as tocool a pulled single crystal. And a heat insulating material 14 isprovided on the outside of the lower end of the graphite cylinder 13 soas to oppose to the raw material melt 6 so that the heat radiation fromthe surface of the raw material melt 6 is intercepted and thetemperature of the surface of the raw material melt 6 is kept.

A polycrystalline material is put in the quartz crucible 7 installed inthe apparatus 1 for producing a single crystal as described above, thecrucible 7 is heated by the graphite heater 10 to melt thepolycrystalline material in the quartz crucible 7. A seed crystal 16fixed by a seed holder 15 connected with the lower end of the wire 5 isimmersed into the raw material melt 6 melted from the polycrystallinematerial. Thereafter, the single crystal 4 having a desired diameter andquality is grown under the seed crystal 16 by rotating and pulling theseed crystal 16. In this case, after bringing the seed crystal 16 intocontact with the raw material melt 6, so-called necking, once forming aneck portion by narrowing the diameter to about 3 mm, is performed, andthen, a dislocation-free crystal is pulled by spreading to a desireddiameter.

A silicon single crystal produced by the CZ Method is mainly used toproduce semiconductor devices. In recent years, semiconductor deviceshave come to be integrated higher and devices have come to be finer.Because devices have come to be finer, a problem of Grown-in defectsintroduced during growth of a crystal has become more important.

Hereafter, Grown-in defects will be explained (see FIG. 5).

In a silicon single crystal, when the growth rate of the crystal isrelatively high, there exist Grown-in defects such as FPD (Flow PatternDefect) and COP (Crystal Originated Particle), which are considered dueto voids consisting of agglomerated vacancy-type point defects, at ahigh density over the entire radial direction of the crystal, and theregion containing these defects is referred to as V (Vacancy) region.Furthermore, when the growth rate is further lowered, along withlowering of the growth rate, an OSF (Oxidation Induced Stacking Fault)region is generated from the periphery of the crystal as a shape of aring. When the growth-rate is further lowered, the OSF ring shrinks tothe center of the wafer and disappears. When the growth rate is furtherlowered, there exist defects such as LSEPD (Large Secco Etch Pit Defect)and LFPD (Large Flow Pattern Defect), which are considered due todislocation loops consisting of agglomerated interstitial silicon atomsat a low density, and the region where these defects exist is referredto as I (Interstitial) region.

In recent years, a region containing no FPD and COP to be generated dueto voids as well as no LSEPD and LFPD to be generated due tointerstitial silicon atoms has been found between the V region and the Iregion and outside the OSF ring. The region is referred to as N(Neutral) region. In addition, it has been found that when furtherclassifying N region, there exist Nv region (the region where a lot ofvacancies exist) adjacent to the outside of OSF ring and Ni region (theregion where a lot of interstitial silicon atoms exist) adjacent to Iregion, and that when performing thermal oxidation treatment, a lot ofoxygen precipitates are generated in the Nv region and little oxygenprecipitates are generated in the Ni region.

Furthermore, it has been found that, after thermal oxidation treatment,there exist a region where defects detected by Cu deposition process areparticularly generated (hereinafter referred to as Cu deposition defectregion) in a portion of the Nv region where oxygen precipitates tend tobe generated. And it has been found that the Cu deposition defect regioncauses deterioration of electric property like oxide dielectricbreakdown voltage characteristics.

It is considered that quantity of introduction of these Grown-in defectsis determined by a parameter of a value of V/G which is a ratio of apulling rate (V) and a temperature gradient (G) at the solid-liquidinterface (for example, see V. V. Voronkov, Journal of Crystal Growth,59 (1982) 625-643). Therefore, by controlling a pulling rate and atemperature gradient so that a value of V/G keeps constant, a singlecrystal occupied by desired defect region or desired defect-free regioncan be pulled.

For example, it is disclosed that, when a silicon single crystal ispulled, a single crystal occupied by defect-free region (for example,see Japanese Patent Laid-open (Kokai) No. H11-147786), and a singlecrystal having an OSF ring or nuclei in an OSF ring in the plane of thecrystal and gettering property (for example, see Japanese PatentLaid-open (Kokai) No. 2000-44388) are pulled by controlling a value ofV/G. Moreover, it is disclosed that a silicon single crystal occupied byI region is pulled by controlling a value of V/G and doping nitrogen(for example, see Japanese Patent Laid-open (Kokai) No. H11-349394), anda single crystal in which a size, density and distribution of defectsare uniform is pulled also with doping nitrogen (for example, seeJapanese Patent Laid-open (Kokai) No. 2002-57160). Then, from thosesingle crystals produced above, for example, a wafer the whole plane ofwhich is N region with excluding V region and I region, a wafer in whichOSF is situated in the periphery, a wafer occupied by N region withoutCu deposition defect region or the like can be produced.

However, for example, when a single crystal the whole plane of which isoccupied by N region is pulled, distribution of defects is practicallyexamined, a value of V/G including the region is obtained and a singlecrystal is pulled at the obtained value of V/G. There are many casesthat the estimated value of V/G is different from a value of V/G that asingle crystal the whole plane of which is N region can be actuallyobtained. Especially, there are such a case that, although a furnacestructure (hot zone: HZ) is prepared so that a temperature gradient G atthe solid-liquid interface becomes large in order to increaseproductivity of a single crystal of desired defect region and/or desireddefect-free region by increasing a pulling rate V, a single crystal withdesired quality can be pulled only when a pulling rate V is actually setlower than the estimated rate V. As explained above, there is a problemthat a precise value of V/G including a desired defect region and/or adesired defect-free region is unknown and it is difficult to obtainefficiently a single crystal with high quality.

DISCLOSURE OF THE INVENTION

The present invention was accomplished in view of the aforementionedcircumstances, and its object is to provide a method for producing asingle crystal in which when a single crystal is pulled with controllinga value of V/G, the value of V/G including a desired defect regionand/or a desired defect-free region is determined more precisely and asingle crystal with desired quality can be more surely pulled.

The present invention was accomplished to achieve the aforementionedobject, and there is provided a method for producing a single crystal byCzochralski method with pulling a seed crystal from a raw material melt,wherein when a pulling rate of pulling a single crystal is defined as V(mm/min), a temperature gradient at a solid-liquid interface is definedas G (K/mm) and a highest temperature at an interface between a crucibleand a raw material melt is defined as Tmax(° C.), at least, a range of avalue of V/G (mm²/K·min) including a desired defect region and/or adesired defect-free region is determined according to the Tmax(° C.),and the single crystal is pulled with controlling a value of V/G(mm²/K·min) within the determined range.

As described above, at least, a value of V/G (mm²/K·min) including adesired defect region and/or a desired defect-free region is correctedaccording to the Tmax(° C.) and a range of the value of V/G isdetermined. By pulling a single crystal with controlling a value of V/G(mm²/K·min) in the determined range, a value of V/G (mm²/K·min)including a desired defect region and/or a desired defect-free regioncan be determined more precisely. Therefore, a single crystal occupiedby a desired defect region and/or a desired defect-free region can bemore surely pulled. In addition, a value of V/G including a desireddefect region and/or a desired defect-free region according to variousapparatuses for producing a single crystal can be estimated precisely.Furthermore, the present invention is useful to design an apparatus forproducing a single crystal. Thereby, an single crystal with desiredquality can be produced with great efficiency.

In addition, the temperature gradient G (K/mm) at a solid-liquidinterface means a temperature gradient in a range from melting point ofa raw material (in the case of silicon, it is 1412° C.) to 1400° C.Moreover, controlling a value of V/G (mm²/K·min) means controlling avalue of V/G over almost the entire radial direction of a crystal(except for the region 0-2 cm from the periphery because it isout-diffusion region).

In this case, it is possible that the single crystal is pulled withcontrolling the value of V/G (mm²/K·min) in a range from−0.000724×Tmax+1.31 to less than −0.000724×Tmax+1.38.

As described above, by pulling the single crystal with controlling thevalue of V/G (mm²/K·min) in a range from −0.000724×Tmax+1.31 to lessthan −0.000724×Tmax+1.38, a single crystal including N region and/or OSFregion can be surely produced.

It is more preferable that by pulling the single crystal withcontrolling the value of V/G (mm²/K·min) in a range from−0.000724×Tmax+1.31 to −0.000724×Tmax+1.37, a single crystal including Nregion can be surely produced.

In this case, it is possible that the single crystal is pulled withcontrolling the value of V/G (mm²/K·min) in a range of−0.000724×Tmax+1.38 or more.

As described above, by pulling the single crystal with controlling thevalue of V/G (mm²/K·min) in a range of −0.000724×Tmax+1.38 or more, asingle crystal excluding OSF ring outside can be surely produced.

In this case, it is possible that the single crystal is pulled withcontrolling the value of V/G (mm²/K·min) in a range from−0.000724×Tmax+1.31 to −0.000724×Tmax+1.35.

As described above, by pulling the single crystal with controlling thevalue of V/G (mm²/K·min) in a range from −0.000724×Tmax+1.31 to−0.000724×Tmax+1.35, a single crystal including N region without Cudeposition defect region can be surely produced.

In these cases, it is preferable that the single crystal is pulled withthe Tmax(° C.) being in a range of 1560° C. or less.

As described above, if the Tmax(° C.) is in a range of 1560° C. or less,the value of V/G becomes large enough. Accordingly, a pulling rate V(mm/min) for pulling a single crystal including a desired defect regionand/or a desired defect-free region can be increased enough,productivity of a single crystal can be improved enough.

In these cases, it is possible that, at least, the Tmax(° C.) is changedby providing a heat insulating material between the crucible containingthe raw material melt and a heater provided so as to surround thecrucible, or by providing a heat insulating material below the crucible.

As described above, at least, by providing a heat insulating materialbetween the crucible containing the raw material melt and a heaterprovided so as to surround the crucible, or by providing a heatinsulating material below the crucible, the Tmax(° C.) can be changed toa desired temperature.

In these cases, a silicon single crystal is pulled as the singlecrystal.

In recent years, because apparatuses for producing a single crystal havebeen diversified, it becomes difficult to precisely determine the valueof V/G including a desired defect region and/or a desired defect-freeregion. Furthermore, demand for quality of a silicon single crystal hascome to be strict. The method for producing a single crystal of thepresent invention is particularly ideal for producing such a siliconsingle crystal.

In these cases, a single crystal with a diameter of 200 mm or more ispulled as the single crystal.

The method for producing a single crystal of the present invention isparticularly ideal for producing a single crystal with a diameter of 200mm or more that has been highly demanded in recent years and has come tobe strict about demand for quality.

A single crystal produced by the method for producing a single crystalof the present invention has high quality.

As explained above, according to the present invention, when a singlecrystal is pulled with controlling a value of V/G, the value of V/Gincluding a desired defect region and/or a desired defect-free regioncan be determined more precisely, thereby a single crystal with desiredquality can be more surely pulled at a high level of productivity.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an apparatus for producing asingle crystal in which heat insulating materials are provided below andat the side of the crucible.

FIG. 2 is a schematic sectional view of a conventional apparatus forproducing a single crystal.

FIG. 3 is a graph showing a range of a value of V/G and Tmax that asingle crystal of a desired defect region and/or a desired defect-freeregion is pulled.

(a) shows a range of a value of V/G and Tmax that a single crystal of Nregion and OSF region is pulled,

(b) shows a range of a value of V/G and Tmax that a single crystal of Vregion is pulled,

and (c) shows a range of a value of V/G and Tmax that a single crystalof N region without Cu deposition defect region is pulled.

FIG. 4 is a graph showing a relationship between a value of V/G at aboundary of Nv region and Ni region and Tmax(° C.).

FIG. 5 is an explanatory view showing a relationship between a growthrate and a distribution of crystal defects.

FIG. 6 is a graph showing a relationship between a value of V/G at aboundary of Nv region and Ni region and a diameter of a crucible.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described.However, the present invention is not limited thereto.

The inventors of the present invention performed thorough investigationsby utilizing experiments, simulations etc. Consequently, it has beenfound that a case that an estimated value of V/G is different from anactual value of V/G, for example, a case that an estimated pulling rateV for pulling a single crystal of a desired defect region and/or adesired defect-free region is different from an actual pulling rate V inspite of pulling a single crystal with the same defect distribution, iscaused when single crystals of a desired defect region and/or a desireddefect-free region are pulled by using furnace structures (hot zone: HZ)with various conformations because a value of V/G including the regionvaries according to HZ respectively. Then, the inventors of the presentinvention considered that if a common parameter that can be used invarious HZs can be found, a more appropriate value of V/G can bedetermined according to HZ respectively. Thus, they accomplished thepresent invention.

Namely, the present invention provides a method for producing a singlecrystal by Czochralski method with pulling a seed crystal from a rawmaterial melt, wherein when a pulling rate of pulling a single crystalis defined as V (mm/min), a temperature gradient at a solid-liquidinterface (from melting point of a raw material to 1400° C.) is definedas G (K/mm) and a highest temperature at an interface between a crucibleand a raw material melt is defined as Tmax(° C.), at least, a range of avalue of V/G (mm²/K·min) including a desired defect region and/or adesired defect-free region is determined according to the Tmax(° C.),and the single crystal is pulled with controlling a value of V/G(mm²/K·min) over almost the entire radial direction of the crystal(except for the region 0-2 cm from the periphery) within the determinedrange.

As described above, in the present invention, not only a value of V/Gbut also a highest temperature Tmax(° C.) at an interface between acrucible and a raw material melt are used as a common parameter forvarious HZs. The Tmax(° C.) can be obtained, for example, by providingthermocouples from the bottom to the periphery of a crucible atintervals of 2 cm and measuring a temperature, or by calculating onsimulation.

FIG. 4 is a graph showing the relationship between a value of V/G at aboundary of Nv region and Ni region and Tmax(° C.). As it is clear fromFIG. 4, because the value of V/G and Tmax(° C.) have good correlation,the Tmax(° C.) turns out to be a very useful parameter for determiningthe value of V/G including a desired defect region and/or a desireddefect-free region. Therefore, in order to determine the value of V/G tobe controlled, correction by the Tmax(° C.) is necessary.

Accordingly, at least, a range of a value of V/G (mm²/K·min) including adesired defect region and/or a desired defect-free region is determinedaccording to Tmax(° C.), and a single crystal is pulled with controllinga value of V/G (mm²/K·min) within the determined range. Thereby, asingle crystal of a desired defect region and/or a desired defect-freeregion can be surely pulled. In addition, a value of V/G (mm²/K·min)including a desired defect region and/or a desired defect-free region isdetermined more precisely according to various HZs respectively.Thereby, when an apparatus with any HZ is used, a crystal with desiredquality can be obtained efficiently and the present invention is usefulto design an apparatus for producing a single crystal.

Then, a range of a value of V/G and Tmax that a single crystal of adesired defect region and/or a desired defect-free region is pulled isinvestigated in detail. The result is shown in FIG. 3. FIG. 3( a) is agraph showing a range of a value of V/G and Tmax that a single crystalof N region and OSF region is pulled. FIG. 3( b) is a graph showing arange of a value of V/G and Tmax that a single crystal of V region ispulled. FIG. 3( c) is a graph showing a range of a value of V/G and Tmaxthat a single crystal of N region without Cu deposition defect region ispulled.

As it is clear from FIG. 3( a), by pulling a single crystal withcontrolling a value of V/G (mm²/K·min) in a range from−0.000724×Tmax+1.31 to less than −0.000724×Tmax+1.38, a single crystalof N region and/or OSF region can be surely pulled.

It is more preferable to pull a single crystal with controlling a valueof V/G (mm²/K·min) in a range from −0.000724×Tmax+1.31 to−0.000724×Tmax+1.37. Thereby, a single crystal of N region can be surelypulled.

As it is clear from FIG. 3( b), by pulling a single crystal withcontrolling a value of V/G (mm²/K·min) in a range of −0.000724×Tmax+1.38or more, a single crystal excluding OSF ring outside can be surelyobtained.

Furthermore, as it is clear from FIG. 3( c), by pulling a single crystalwith controlling a value of V/G (mm²/K·min) in a range from−0.000724×Tmax+1.31 to −0.000724×Tmax+1.35, a single crystal including Nregion without Cu deposition defect region can be more surely obtained.

In addition, as it is clear from FIG. 3( a)-(c), by setting the Tmax(°C.) in a range of 1560° C. or less, a value of V/G (mm²/K·min) includinga desired defect region and/or a desired defect-free region can besufficiently high. For example, as shown in FIGS. 3( a) and (c), whenthe Tmax(° C.) is 1560° C. or less, it is found that the value of V/G(mm²/K·min) at a boundary of I region and N region can be of a highvalue of 0.18 or more. Therefore, a single crystal with desired qualitycan be produced at a high level of productivity.

A highest temperature Tmax(° C.) at an interface between a crucible anda raw material melt can be changed by changing HZ.

For example, the Tmax(° C.) is changed to a desired range, at least, byproviding a heat insulating material between the crucible containing theraw material melt and a heater provided so as to surround the crucible,or by providing a heat insulating material below the crucible.

For example, an apparatus 1 for producing a single crystal in which heatinsulating materials are provided below and at the side of a crucible isshown in FIG. 1. The apparatus 1 for producing a single crystal isalmost the same as the apparatus for producing a single crystal as shownin FIG. 2 except that the heat insulating materials 17 are providedbelow and at the side of the crucible. Namely, in the apparatus 1 forproducing a single crystal, in the main chamber 2, the single crystal 4,the raw material melt 6, the quartz crucible 7, the graphite crucible 8,the shaft 9, the graphite heater 10, the heat insulating member 11, thegraphite cylinder 13, the heat insulating material 14 and the heatinsulating material 17 for the crucible are shown here. In thesecomponents, particularly, by providing a heat insulating material 17 forthe crucible with varying numbers, a size, position, material etc., theTmax (° C.) can be changed to a desired range.

In addition, the Tmax(° C.) can also be changed by changing a size of acrucible. For example, if a size of a crucible is smaller, the Tmax(°C.) can be set lower. Therefore, by making a size of a crucible smaller,a value of V/G including a desired defect region and/or a desireddefect-free region can be set higher as shown in FIG. 6. For example, ifthe size of a crucible is set larger than a diameter of a single crystalto be pulled but not larger than 2.5 times the diameter of the singlecrystal, then the Tmax(° C.) can be low enough. Therefore, a value ofV/G including a desired defect region and/or a desired defect-freeregion can be set in a high range enough.

In recent years, because apparatuses for producing a single crystal havebeen even more diversified, it has become difficult to preciselydetermine a value of V/G including a desired defect region and/or adesired defect-free region. Furthermore, demand for quality of a siliconsingle crystal has come to be strict. The method for producing a singlecrystal of the present invention as described above is particularlyideal for producing such a silicon single crystal.

Furthermore, the method for producing a single crystal of the presentinvention is particularly ideal for producing a single crystal with adiameter of 200 mm or more that has been highly demanded in recent yearsand has come to be strict about demand for quality.

And a single crystal produced by the method for producing a singlecrystal of the present invention has high quality.

Hereinafter, the present invention will be explained further in detailwith reference to Examples.

EXAMPLE 1

Using an apparatus for producing a single crystal, which has thecrucible with a diameter of 600 mm (24 inches), as shown in FIG. 1, asilicon single crystal with a diameter of 8 inches (200 mm) was pulledso that the whole plane of the crystal would be N region without Cudeposition defect region.

For that purpose, firstly, heat insulating materials were provided belowand at the side of the crucible, the highest temperature Tmax(° C.) atan interface between the crucible and a raw material melt was set at1514 (° C.). In order to produce a single crystal including N regionwithout Cu deposition defect region when the Tmax(° C.) is set above, arange of a value of V/G (mm²/K·min) should be in the range from 0.21 to0.25 (from −0.000724×1514+1.31 to −0.000724×1514+1.35) (See FIG. 3( c)).Accordingly, the range from 0.22 to 0.24 was selected as a range of avalue of V/G (mm²/K·min) to unfailingly pull a single crystal the wholeplane of which is occupied by N region without Cu deposition defectregion. Next, a single crystal was pulled with controlling a value ofV/G (mm²/K·min) within the selected range. Namely, because a temperaturegradient G at an solid-liquid interface in the HZ of the apparatus A forproducing a single crystal was 2.337 K/mm, the single crystal was pulledwith controlling a pulling rate V from 0.51 mm/min to 0.56 mm/min.

The silicon single crystal pulled as described above was examined and itwas found that the whole plane of the crystal was occupied by N regionwithout Cu deposition defect region and the crystal had high quality.

EXAMPLE 2

Using the same apparatus for producing a single crystal as Example 1, asilicon single crystal with a diameter of 8 inches (200 mm) was pulledso that the whole plane of the crystal would be N region without Cudeposition defect region. However, heat insulating materials which canchange a highest temperature Tmax (° C.) at an interface between acrucible and a raw material melt were not provided.

In the apparatus for producing a single crystal, the highest temperatureTmax(° C.) at an interface between a crucible and a raw material meltwas 1560 (° C.). In order to produce a single crystal including N regionwithout Cu deposition defect region with the Tmax(° C.), a range of avalue of V/G (mm²/K·min) should be in the range from 0.18 to 0.22 (from−0.000724×1560+1.31 to −0.000724×1560+1.35). Accordingly, the range from0.19 to 0.21 was selected as a range of a value of V/G (mm²/K·min) tounfailingly pull a single crystal the whole plane of which is occupiedby N region without Cu deposition defect region. Next, a single crystalwas pulled with controlling a value of V/G (mm²/K·min) within theselected range. Namely, because a temperature gradient G at asolid-liquid interface in the HZ of the apparatus for producing a singlecrystal was 2.500 K/mm, the single crystal was pulled with controlling apulling rate V from 0.48 mm/min to 0.53 mm/min.

The silicon single crystal pulled as described above was examined and itwas found that the whole plane of the crystal was occupied by N regionwithout Cu deposition defect region and the crystal had high quality.

EXAMPLE 3

Using a different apparatus for producing a single crystal, which has acrucible with a diameter of 750 mm (30 inches), from that of Example 1and 2, a silicon single crystal with a diameter of 8 inches (200 mm) waspulled so that the whole plane of the crystal would be N region withoutCu deposition defect region.

In the apparatus for producing a single crystal, the highest temperatureTmax(° C.) at an interface between the crucible and a raw material meltwas 1600° C. In order to produce a single crystal including N regionwithout Cu deposition defect region with the Tmax(° C.), a range of avalue of V/G (mm²/K·min) should be in the range from 0.15 to 0.19 (from−0.000724×1600+1.31 to −0.000724×1600+1.35). Accordingly, the range from0.16 to 0.18 was selected as a range of a value of V/G (mm²/K·min) tounfailingly pull a single crystal the whole plane of which is occupiedby N region without Cu deposition defect region. Next, a single crystalwas pulled with controlling a value of V/G (mm²/K·min) within theselected range. Namely, because a temperature gradient G at asolid-liquid interface in the HZ of the apparatus for producing a singlecrystal was 2.674 K/mm, the single crystal was pulled with controlling apulling rate V from 0.43 mm/min to 0.48 mm/min.

The silicon single crystal pulled as described above was examined and itwas found that the whole plane of the crystal was occupied by N regionwithout Cu deposition defect region and the crystal had high quality.

EXAMPLE 4

Using almost the same apparatus for producing a single crystal asExample 1, a silicon single crystal with a diameter of 8 inches (200 mm)was pulled so that the whole plane of the crystal would not bedefect-free region, but with excluding OSF ring outside, almost over theentire radial direction of the crystal would be V region. However, inthe apparatus for producing a single crystal used here, the position ofa heat insulating material 14 was adjusted so that the distance betweenthe surface of a raw material melt 6 and the lower end of the heatinsulating material 14 was as half as that of the apparatus forproducing a single crystal of Example 1.

In the apparatus for producing a single crystal, the highest temperatureTmax(° C.) at an interface between the crucible and the raw materialmelt was 1514° C. In order to produce a single crystal almost over theentire radial direction of which include V region with the Tmax(° C.), arange of a value of V/G (mm²/K·min) should be in the range of 0.28 ormore (−0.000724×1514+1.38 or more). And, a value of V/G (mm²/K·min)needs to be in a range of 1.90 or less (−0.000724×1514+3.0 or less) thata single crystal can be grown without being deformed. Accordingly, therange from 0.29 to 0.31 was selected as a range of a value of V/G(mm²/K·min) to unfailingly pull a single crystal almost over the entireradial direction of which include V region. Next, a single crystal waspulled with controlling a value of V/G (mm²/K·min) within the selectedrange. Namely, because the maximum temperature gradient G at asolid-liquid interface in the HZ of the apparatus for producing a singlecrystal was 4.07 K/mm, the single crystal was pulled with controlling apulling rate V from 1.18 mm/min to 1.26 mm/min.

The silicon single crystal pulled as described above was examined and itwas confirmed that OSF ring was surely excluded almost over the entireradial direction of the single crystal.

As it is clear from Examples 1-3, by using a highest temperature Tmax(°C.) at an interface between a crucible and a raw material melt as aparameter to determine a value of V/G, a value of V/G including N regionwithout Cu deposition defect region was precisely determined accordingto an apparatus for producing a single crystal respectively.Accordingly, by controlling a value of V/G as determined above, a singlecrystal including N region without Cu deposition defect region can besurely pulled. In addition, as it is clear from Examples 1 and 2, byproviding heat insulating materials and changing Tmax (° C.) to lowertemperature, a value of V/G including N region without Cu depositiondefect region could be set higher. Accordingly, a pulling rate V couldbe set higher, and thus productivity of a single crystal could beimproved.

In addition, the present invention is not limited to the embodimentdescribed above. The above-described embodiment is mere an example, andthose having substantially the same structure as technical ideasdescribed in the appended claims and providing the similar functions andadvantages are included in the scope of the present invention.

For example, in the present invention, the method for producing a singlecrystal was explained in the case of not doping impurities such asnitrogen and carbon (non-dope). However, in the case of dopingimpurities such as nitrogen and carbon, although a value of V/G differsconsiderably from the case of non-dope, a value of V/G has the samerelationship with Tmax in such a case, too. Therefore, to correct onTmax for a value of V/G including defect regions that changes accordingto respective impurities and their concentrations are included in thescope of the present invention.

1. A method for producing a single crystal by Czochralski method by pulling a seed crystal from a raw material melt, comprising: immersing the seed crystal into the raw material melt; and growing the single crystal by rotating and pulling the seed crystal, wherein: the single crystal is pulled while controlling a value of V/G (mm²/K·min) within a range of values of V/G (mm²/K·min); and the range of values of V/G (mm²/K·min), including a defect region and/or a defect-free region, is controlled according to Tmax(° C.); wherein: V (mm/min) is a single crystal pulling rate of pulling the single crystal; G (K/mm) is a temperature gradient at a solid-liquid interface, in a range of a melting point of the raw material and 1400° C.; Tmax(° C.) is a highest temperature of the raw material melt at an interface between a quartz crucible inner wall and the raw material melt; and the range of values of V/G (mm²/K·min) is: (A) from −0.000724 [mm²/(° C.·K·min)]×Tmax(° C.)+1.31 (mm²/K·min) to less than −0.000724 [mm²/(° C.·K·min)]×Tmax(° C.)+1.38 (mm²/K·min); or (B) −0.000724 [mm²/(° C.·K·min)]×Tmax(° C.)+1.38 (mm²/K·min) or more; or (C) from −0.000724 [mm²/(° C.·K·min)]×Tmax(° C.)+1.31 (mm²/K·min) to −0.000724 [mm²/(° C.·K·min)]×Tmax(° C.)+1.35 (mm²/K·min).
 2. The method for producing a single crystal according to claim 1, wherein the single crystal is pulled with the Tmax(° C.) being in a range of 1560° C. or less.
 3. The method for producing a single crystal according to claim 1, wherein, at least, the Tmax(° C.) is changed by providing a heat insulating material between the crucible containing the raw material melt and a heater provided so as to surround the crucible, or by providing a heat insulating material below the crucible.
 4. The method for producing a single crystal according to claim 2, wherein, at least, the Tmax(° C.) is changed by providing a heat insulating material between the crucible containing the raw material melt and a heater provided so as to surround the crucible, or by providing a heat insulating material below the crucible.
 5. The method of producing a single crystal according to claim 1, wherein the single crystal that is pulled is a silicon single crystal.
 6. The method of producing a single crystal according to claim 1, wherein the single crystal that is pulled has a diameter of 200 mm or more. 